Microtubule-Dependent Alterations to Mechanical Properties and Mechanotransduction in Skeletal Muscle

Abstract

In striated muscle, we discovered that force transduced through the microtubule (MT) network activates NADPH Oxidase 2 (NoX2) ROS signals (i.e., X-ROS) that target calcium (Ca2+) channels. The significance of our discovery was revealed in dystrophin-deficient heart and skeletal muscle, where MT proliferation leads to an increase in both the cytoskeletal stiffness and the mechano-activated X-ROS and Ca2+ signaling that underscores disease progression and enhanced contraction-induced injury. Our most recent work (Kerr, J.P., et. al., Nat. Comm. http://dx.doi.org/10.1038/ncomms9526) implicated the abundance of detyrosinated MT filaments, rather than MT network proliferation per se, in the amplification of X-ROS mechanotransduction and depressed contractile mechanics through the alteration of cytoskeletal stiffness. Further, reducing MT detyrosination in vivo protected against contraction-induced injury in the mdx mouse, highlighting the significance of X-ROS and detyrosinated MT in the disease process. Here we extend our discovery by examining the passive mechanical properties of single, intact skeletal myofibers using novel technology and techniques. We show that the longitudinal stress-strain relationship and shear stiffness of the muscle fiber is regulated by the abundance of detyrosinated MTs. These results are consistent with the MT network acting as a compression-resistant element both within the myofilament lattice and beneath the sarcolemmal membrane, and that detyrosination of the MT network ‘tunes’ this behavior. Our ongoing studies will inform an integrated understanding and computational modeling of the cytoskeleton's role in cell mechanics and mechanotransduction, forwarding our goal of defining novel therapeutic targets for disease.